1. Field of the Invention
The present invention relates to a refrigerator comprising a refrigerating cycle using a hydrofluorocarbon type refrigerant not containing chlorine such as 1,1,1,2-tetrafluoroethane (hereinafter referred to as R134a) or a refrigerant mixture thereof, having a polyvinyl ether oil as the base oil.
2. Background Art
Many of the conventional refrigerators and compressors for automatic vendors or show-cases used dichlorodifluoromethane (hereinafter referred to as R12). R12 has been under the flon regulation for preventing the ozone layer destruction. As a substitute refrigerant for R12, hydrofluorocarbon type refrigerants (HFC type, FC type) not containing chlorine represented by R134a are studied for the use of a refrigerator (see the official gazette of Japanese Patent Application Laid-Open (JP-A) No. 1-271491).
However, since the refrigerant R134a is poor in terms of compatibility with conventionally-used refrigerator oils, such as a mineral oil and an alkyl benzene oil, there is a problem of poor lubrication of a compressor due to deterioration of oil return to the compressor and inhalation of separated refrigerant at the time of starting after interval.
Therefore, the present inventors discussed the application of a polyol ester oil, which is compatible with the refrigerant R134a as the refrigerator oil. However, it is known that the polyol ester oil generates an aliphatic acid by thermal decomposition to cause corrosion in sliding members, which leads to abrasion.
Then the present inventors elaborately studied a combination of R134a as the refrigerant and a polyol ester oil as the refrigerator oil for the application in a refrigerant compressor. As a result, it was learned that in addition to the above-mentioned problem, a polyol ester oil is hydrolyzed by moisture to raise the total acid number so that metal soap is generated to be sludge and casts adverse effect on the refrigerating cycle, or is decomposed, oxidized to be deteriorated, and polymerized to generate metal soap or polymer sludge and casts adverse effect on the refrigerating cycle.
On the other hand, although it is known that a polyoxyalkylene glycol oil is not hydrolyzed and does not require strict care, due to its poor insulating property, it can not be used appropriately as it is in this kind of a refrigerant compressor comprising such a motor.
Then the present inventors found out that the above-mentioned problems can be solved by adding a certain additive to a polyvinyl ether oil with a special composition and combining with a certain HFC type refrigerant with a certain care.
An object of the present invention is to obtain a good refrigerator using polyvinyl ether oil as a refrigerator oil, which is compatible with a hydrofluorocarbon type refrigerant not containing chlorine (such as R134a) without suffering the above-mentioned problems.
A refrigerator according to claim 1 comprises a refrigerating cycle using a hydrofluorocarbon type refrigerant not containing chlorine or a refrigerant mixture thereof, with a refrigerator oil compatible with the refrigerant sealed, wherein the refrigerator oil comprises a polyvinyl ether type compound having a structural unit represented by the general formula (1) as the main component, with a pour point of xe2x88x9240xc2x0 C. or less, a two-liquid separation temperature of xe2x88x9220xc2x0 C. or less, a total acid number of 0.02 mgKOH/g or less, a viscosity of 8 to 100 cst at 40xc2x0 C. or less, and a viscosity index of 80 or more, 
wherein n is an integral number in the range of 1 or more, R1 to R3 are each a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms and may be the same or different, R4 is an alkyl group having 1 to 4 carbon atoms, and units in which R4 is an alkyl group having 1 to 2 carbon atoms are 40 to 100% and units in which R4 is an alkyl group having 3 to 4 carbon atoms are 0 to 60%.
In a refrigerator according to claim 2, the hydrofluorocarbon type refrigerant has a purity of 99.5% by weight or more, with the content of a chlorine type refrigerant of 2000 ppm or less.
In a refrigerator according to claim 3, the equilibrium moisture in the refrigerating cycle represented by the equation (2) is 200 ppm or less:                                           (                          residual              ⁢                              xe2x80x83                            ⁢              moisture              ⁢                              xe2x80x83                            ⁢              content              ⁢                              xe2x80x83                            ⁢              in              ⁢                              xe2x80x83                            ⁢              the              ⁢                              xe2x80x83                            ⁢              refrigerating              ⁢                              xe2x80x83                            ⁢              cycle                        )                                (                                          filled                ⁢                                  xe2x80x83                                ⁢                oil                ⁢                                  xe2x80x83                                ⁢                amount                            +                              filled                ⁢                                  xe2x80x83                                ⁢                refrigerant                ⁢                                  xe2x80x83                                ⁢                amount                                      )                          xc3x97                  10          6                ⁢        ppm                            (        2        )            
In a refrigerator according to claim 4, the residual oxygen content in the refrigerating cycle is 0.2% by weight or less with respect to the content volume of the refrigerating cycle.
In a refrigerator according to claim 5, the refrigerator oil contains 0.01 to 1.0% by weight of a phenol type antioxidant as an essential component and 0.01 to 2% by weight of an epoxy type or carbodiimide type compound with respect to its oil content.
In a refrigerator according to claim 6, the refrigerator oil contains 0.1 to 2% by weight of a phosphoric acid ester type compound with respect to its oil content.
In a refrigerator according to claim 7, the refrigerant is a 1,1,1,2-tetrafluoroethane (R134a), an azetropic mixture refrigerant containing 50% by weight of difluoromethane (R32) and 50% by weight of pentafluoroethane (R125), or a pseudoazetropic mixture refrigerant containing 44% by weight of pentafluoroethane (R125), 52% by weight of trifluoroethane (R143a) and 4% by weight of 1,1,1,2-tetrafluoroethane (R134a).
A refrigerator according to claim 8 comprises a compressor unit sealed in a hermetically sealed container, with an HFC type refrigerant or a refrigerant mixture thereof and a refrigerator oil compatible with the refrigerant sealed in the hermetically sealed container, wherein the refrigerator oil comprises a polyvinyl ether type compound having a structural unit represented by the general formula (1) as the main component, with a pour point of xe2x88x9240xc2x0 C. or less, a two-liquid separation temperature of xe2x88x9220xc2x0 C. or less, a total acid number of 0.02 mgKOH/g or less, a viscosity of 8 to 100 cst at 40xc2x0 C. or less, and a viscosity index of 80 or more, 
wherein n is an integral number in the range of 1 or more, R1 to R3 are each a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms and may be the same or different, R4 is an alkyl group having 1 to 4 carbon atoms, and units in which R4 is an alkyl group having 1 to 2 carbon atoms are 80 to 100% and units in which R4 is an alkyl group having 3 to 4 carbon atoms are 0 to 20%.
In a refrigerator according to claim 9, the hydrofluorocarbon type refrigerant has a purity of 99.5% by weight or more, with the content of a chlorine type refrigerant of 2000 ppm or less.
In a refrigerator according to claim 10, the equilibrium moisture in the refrigerating cycle represented by the formula (2) is 200 ppm or less:                                           (                          residual              ⁢                              xe2x80x83                            ⁢              moisture              ⁢                              xe2x80x83                            ⁢              content              ⁢                              xe2x80x83                            ⁢              in              ⁢                              xe2x80x83                            ⁢              the              ⁢                              xe2x80x83                            ⁢              refrigerating              ⁢                              xe2x80x83                            ⁢              cycle                        )                                (                                          filled                ⁢                                  xe2x80x83                                ⁢                oil                ⁢                                  xe2x80x83                                ⁢                amount                            +                              filled                ⁢                                  xe2x80x83                                ⁢                refrigerant                ⁢                                  xe2x80x83                                ⁢                amount                                      )                          xc3x97                  10          6                ⁢        ppm                            (        2        )            
In a refrigerator according to claim 11, the residual oxygen content in the refrigerating cycle is 0.2% by weight or less with respect to the content volume of the refrigerating cycle.
In a refrigerator according to claim 12, the refrigerant comprises at least two compounds selected from the group consisting of hydrofluorocarbon types represented by the general formula (3):
ClHmFnxe2x80x83xe2x80x83(3)
wherein when 1=1, m=1xcx9c2, n=2xcx9c3 and m+n=4, when 1=2, m=1xcx9c4, n=2xcx9c5 and m+n=6, and when 1=3, m=1xcx9c3, n=5xcx9c7 and m+n=8.
In a refrigerator according to claim 13, the refrigerant is an azetropic mixture refrigerant containing 50% by weight of difluoromethane (R32) and 50% by weight of pentafluoroethane (R125), or a pseudoazetropic mixture refrigerant containing 44% by weight of pentafluoroethane (R125), 52% by weight of trifluoroethane (R143a) and 4% by weight of 1,1,1,2-tetrafluoroethane (R134a).
In a refrigerator according to claim 14, the refrigerator oil contains 0.01 to 1.0% by weight of a phenol type antioxidant as an essential component and 0.01 to 2% by weight of an epoxy type or carbodiimide type compound with respect to its oil content.
In a refrigerator according to claim 15, the refrigerator oil contains 0.1 to 2% by weight of a phosphoric acid ester type compound with respect to its oil content.
A refrigerator according to claim 16 comprises a compressor unit sealed in a hermetically sealed container, with an HFC type refrigerant or a refrigerant mixture thereof and a refrigerator oil compatible with the refrigerant sealed in the hermetically sealed container, wherein the refrigerator oil comprises a polyvinyl ether type compound having a structural unit represented by the general formula (1) as the main component, with a pour point of xe2x88x9240xc2x0 C. or less, a two-liquid separation temperature of xe2x88x9220xc2x0 C. or less, a total acid number of 0.02 mgKOH/g or less, a viscosity of 8 to 100 cst at 40xc2x0 C. or less, and a viscosity index of 80 or more, 
wherein n is an integral number in the range of 1 or more, R1 to R3 are each a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms and may be the same or different, R4 is an alkyl group having 1 to 4 carbon atoms, and units in which R4 is an alkyl group having 1 to 2 carbon atoms are 60 to 100% and units in which R4 is an alkyl group having 3 to 4 carbon atoms are 0 to 40%.
In a refrigerator according to claim 17, the hydrofluorocarbon type refrigerant has a purity of 99.5% by weight or more, with the content of a chlorine type refrigerant of 2000 ppm or less.
In a refrigerator according to claim 18, the equilibrium moisture in the refrigerating cycle represented by the formula (2) is 200 ppm or less:                                           (                          residual              ⁢                              xe2x80x83                            ⁢              moisture              ⁢                              xe2x80x83                            ⁢              content              ⁢                              xe2x80x83                            ⁢              in              ⁢                              xe2x80x83                            ⁢              the              ⁢                              xe2x80x83                            ⁢              refrigerating              ⁢                              xe2x80x83                            ⁢              cycle                        )                                (                                          filled                ⁢                                  xe2x80x83                                ⁢                oil                ⁢                                  xe2x80x83                                ⁢                amount                            +                              filled                ⁢                                  xe2x80x83                                ⁢                refrigerant                ⁢                                  xe2x80x83                                ⁢                amount                                      )                          xc3x97                  10          6                ⁢        ppm                            (        2        )            
In a refrigerator according to claim 19, the residual oxygen content in the refrigerating cycle is 0.2% by weight or less with respect to the content volume of the refrigerating cycle.
In a refrigerator according to claim 20, the refrigerant comprises at least two compounds selected from the group consisting of hydrofluorocarbon types represented by the general formula (3):
ClHmFnxe2x80x83xe2x80x83(3)
wherein when 1=1, m=1xcx9c2, n=2xcx9c3 and m+n=4, when 1=2, m=1xcx9c4, n=2xcx9c5 and m+n=6, and when 1=3, m=1xcx9c3, n=5xcx9c7 and m+n=8.
In a refrigerator according to claim 21, the refrigerant is a pseudoazetropic mixture refrigerant containing 23% by weight of difluoromethane (R32), 25% by weight of pentafluoroethane (R125), 52% by weight of 1,1,1,2-tetrafluoroethane (R134a), or a pseudeoazeotropic mixture refrigerant containing 25% by weight of difluoromethane (R32), 15% by weight of pentafluoroethane (R125), 60% by weight of 1,1,1,2-tetrafluoroethane (R134a).
In a refrigerator according to claim 22, the refrigerator oil contains 0.01 to 1.0% by weight of a phenol type antioxidant as an essential component and 0.01 to 2% by weight of an epoxy type or carbodiimide type compound with respect to its oil content.
In a refrigerator according to claim 23, the refrigerator oil contains 0.1 to 2% by weight of a phosphoric acid ester type compound with respect to its oil content.
A refrigerator according to claim 24 comprises a refrigerant compressor, a condenser, an expansion device, and an evaporator, connected to each other with pipes, with an HFC type refrigerant or a refrigerant mixture thereof and a refrigerator oil compatible with the refrigerant sealed in a hermetically sealed container, wherein the refrigerator oil comprises a polyvinyl ether type compound having a structural unit represented as the main component, with a pour point of xe2x88x9240xc2x0 C. or less, a two-liquid separation temperature of xe2x88x9220xc2x0 C. or less, a total acid number of 0.02 mgKOH/g or less, a viscosity of 8 to 100 cst at 40xc2x0 C. or less, and a viscosity index of 80 or more. 
wherein n is an integral number in the range of 1 or more, R1 to R3 are each a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms and may be the same or different, R4 is an alkyl group having 1 to 4 carbon atoms, and units in which R4 is an alkyl group having 1 to 2 carbon atoms are 40 to 100% and units in which R4 is an alkyl group having 3 to 4 carbon atoms are 0 to 60%.